Multi-ratio transmission

ABSTRACT

A transmission comprising gear sets (P 1 , P 2 , P 3 , P 4 ), eight shafts and six shift elements. Sun gear of set (P 1 ) couples the drive shaft, the carrier of set (P 1 ) is connected to shaft ( 3 ) which couples a housing, via a first brake, and couples the drive shaft and shaft ( 5 ) respectively via clutches. Shaft ( 5 ) couples the ring gear of set (P 2 ), the sun gears of sets (P 3 , P 4 ), and the drive shaft couples the carrier of set (P 4 ). Shaft ( 6 ) couples the ring gear of set (P 1 ) and the carrier of set (P 2 ). Sun gear of set (P 2 ) is connected to shaft ( 4 ) which couples a housing, via a brake. Ring gear of set (P 3 ) couples the housing, the output shaft couples, via a clutch, shaft ( 7 ) which couples the ring gear of set (P 4 ), and, via another clutch, shaft ( 8 ) which couples the carrier of set (P 3 ).

This application is a National Stage completion of PCT/EP2010/062129filed Aug. 19, 2010, which claims priority from German Application No.10 2009 028 709.4 filed Aug. 20, 2009.

FIELD OF THE INVENTION

The present invention relates to a multi-stage transmission of aplanetary design, in particular an automatic transmission for a motorvehicle, according to the preamble of claim 1.

BACKGROUND OF THE INVENTION

According to the prior art, automatic transmissions, particularly formotor vehicles, comprise planetary gear sets that are shifted usingfriction elements or shift elements such as clutches and brakes, andtypically are connected to a start-up element, such as a hydrodynamictorque converter or a fluid coupling, that is subject to a slip effectand is provided optionally with a lock-up clutch.

Such an automatic transmission is known, for example, from theapplicant's patent DE 199 49 507 A1, according to which twonon-shiftable front-mounted gear sets are provided on the drive shaftand generate two rotational speeds on the output side, which, inaddition to the rotational speed of the drive shaft, can be selectivelymeshed with a shiftable double planetary gear set acting on the outputshaft by selective engagement of the shift elements such that only oneof the two currently actuated shift elements must be engaged ordisengaged to shift from one gear to the next higher or lower gear.

By using five shift elements, seven forward gears are obtained; by usingsix shift elements, nine or ten forward gears are obtained.

Furthermore, patent DE 102 13 820 A1 makes known a multi-speed automatictransmission with eight forward gears and one reverse gear, whichcomprises a first input path T1 of a first transmission ratio; an inputpath T2 that has a higher transmission ratio than that of input path T1;a Ravigneaux type planetary gear set with four elements, namely, a firstelement, a second element, a third element and a fourth element in thesequence of elements in a rotational speed diagram; a clutch C-2 whichtransfers rotation of the input path T2 to the first element S3; aclutch C-1, which transfers rotation from the input path T2 to thefourth element S2; a clutch C-4, which transfers rotation from the inputpath T1 to the first element; a clutch C-3, which transfers rotationfrom the input path T1 to the second element C3; a brake B-1, whichproduces meshing of the fourth element; a brake B-2, which producesmeshing of the second element; and an output element that is coupled tothe third element S3.

Furthermore, a nine-speed multi-step transmission is known from DE 29 36969 A1; it comprises eight shift elements and four gear sets, whereinone gear set serves as a front-mounted gear set and the main gearingincludes a Simpson set and a further gear set serving as reversegearing.

Further multi-step transmissions are known, for example, from theapplicant's DE 102005010210 A1 and DE 102006006637 A1.

Automatically shiftable vehicle transmissions, of the planetary design,are already generally described numerous times in the prior art and arecontinually undergoing further development and improvement. Thesetransmissions should have a relatively simple design, in particularrequiring a low number of shift elements, and minimize the need fordouble shifting when sequential shifting is performed, thereby ensuringthat only one shift element is ever switched when shifting is performedin defined groups of gears.

The applicant's document, DE 102008000428.3 which is not yet published,discloses a multi-step transmission of a planetary design that includesan input shaft and an output shaft which are disposed in a housing. Theknown transmission includes at least four planetary gear sets which aredesignated, in the following, as the first, second, third, and fourthplanetary gear set, at least eight rotatable shafts which are designatedin the following as the drive shaft, output shaft, third, fourth, fifth,sixth, seventh, and eighth shaft, and at least six shift elementscomprising brakes and clutches, whose selected engagement producesdifferent transmission ratios between the input shaft and the outputshaft, and therefore preferably nine forward gears and one reverse gearcan be realized.

The first and second planetary gear sets, which are preferably designedas minus planetary gear sets, form a shiftable front-mounted gear set,wherein the third and fourth planetary gear sets form a main gear set.

In the known multi-step transmission, the carriers of the first andsecond planetary gear sets are coupled together via the fourth shaftwhich is connected to an element of the main gear set, the ring gear ofthe first planetary gear set is coupled to the sun gear of the secondplanetary gear set via the eighth shaft, which is detachably connectableto the drive shaft via the first clutch, and the sun gear of the firstplanetary gear set can be coupled to a housing of the transmission bymeans of the third shaft, via a first brake, and is detachablyconnectable to the drive shaft via a second clutch, wherein the ringgear of the second planetary gear set can be coupled to a housing of thetransmission by means of the fifth shaft via a second brake. Inaddition, the seventh shaft is constantly connected to at least oneelement of the main gear set, and can be coupled to a housing of thetransmission via a third brake, wherein the sixth shaft is constantlyconnected to at least one further element of the main gear set and isdetachably connectable to the drive shaft, via a third clutch; theoutput shaft is constantly connected at least to one further element ofthe main gear set.

In the known transmission, the fourth shaft is preferably constantlyconnected to the ring gear of the third planetary gear set, wherein thesixth shaft is constantly connected to the ring gear of the fourthplanetary gear set and to the carrier of the third planetary gear set,and is detachably connectable to the drive shaft via the third clutch.Furthermore, the seventh shaft is constantly connected to the sun gearsof the third and fourth planetary gear sets, and can be coupled to ahousing of the transmission via the third brake. In this case, theoutput drive is produced via the output shaft that is constantlyconnected to the carrier of the fourth planetary gear set. Furthermore,the third and fourth planetary gear sets can be combined or reduced to aRavigneaux set having a common carrier and a common ring gear.

SUMMARY

The object of the present invention is to propose a multi-steptransmission of the initially described type, which has nine forwardgears and at least one reverse gear having a sufficient transmissionratio, in which the design complexity and the overall size, inparticular the overall length and the weight, are optimized, and inwhich efficiency is improved with respect to drag losses and gearinglosses. In addition, in the multi-step transmission according to theinvention, minimal support moments should act on the shift elements. Thetransmission, according to the invention, should be particularly suitedfor a front transverse installation.

Accordingly, a multi-step transmission, according to the invention, of aplanetary design is proposed which has an input shaft and an outputshaft which are disposed in a housing. In addition, there are providedat least four planetary gear sets which are designated, in thefollowing, as the first, second, third, and fourth planetary gear sets,eight rotatable shafts which are designated, in the following, as thedrive shaft, output shaft, third, fourth, fifth, sixth, seventh, andeighth shaft, and at least six shift elements comprising brakes andclutches, whose selected engagement produces different transmissionratios between the drive shaft and the output shaft, and thereforepreferably nine forward gears and one reverse gear can be realized.

The planetary gear sets, viewed axially, are disposed in the sequence offirst planetary gear set, second planetary gear set, third planetarygear set, fourth planetary gear set, and are preferably designed asminus planetary gear sets.

As is well known, a simple minus planetary gear set comprises a sungear, a ring gear, and a carrier on which the planetary gears arerotatably supported, the planetary gears meshing with the sun gear andthe ring gear. As a result, when the carrier is fixed, the ring gear hasa direction of rotation that is opposite that of the sun gear. Incontrast, a simple plus planetary gear set comprises a sun gear, a ringgear and a carrier, on which inner and outer planet gears are rotatablysupported, wherein all inner planet gears mesh with the sun gear and allouter planet gears mesh with the ring gear, wherein each inner planetgear meshes with only one outer planet gear. As a result, when thecarrier is fixed, the ring gear has the same direction of rotation asthe sun gear.

According to a preferred embodiment of the invention, the sun gear ofthe first planetary gear set is connected to the drive shaft, whereinthe carrier of the first planetary gear set is connected to the thirdshaft which can be coupled to a housing of the transmission via a firstbrake and is detachably connected to the fifth shaft via a secondclutch, wherein the fifth shaft is connected to the ring gear of thesecond planetary gear set, to the sun gear of the third planetary gearset, and to the sun gear of the fourth planetary gear set, and the driveshaft is connected to the carrier of the fourth planetary gear set.

Furthermore, the ring gear of the first planetary gear set is connectedto the sixth shaft, which is connected to the carrier of the secondplanetary gear set, the ring gear of the third planetary gear set iscoupled to a housing of the transmission, the sun gear of the secondplanetary gear set is connected to the fourth shaft, which can becoupled to a housing of the transmission via a second brake, and whereinthe output shaft is detachably connectable, via a third clutch, to theseventh shaft, which is connected to the ring gear of the fourthplanetary gear set, and, via a fourth clutch, to the eighth shaft, whichis connected to the carrier of the third planetary gear set.

It is provided that the first planetary gear set can be blocked byengaging a first clutch, wherein the first clutch is preferably designedas a clutch that detachably connects the third shaft to the drive shaft,or as a clutch that detachably connects the third shaft to the sixthshaft.

The embodiment of the multi-step transmission, according to theinvention, results in transmission ratios that are particularly suitablefor passenger vehicles, and in a greater overall gear ratio of themulti-step transmission, thereby improving driving smoothness andsignificantly reducing fuel consumption.

Furthermore, design complexity is significantly reduced with themulti-step transmission, according to the invention, due to a low numberof shift elements. Using the multi-step transmission according to theinvention, it is advantageously possible to perform a start-up using ahydrodynamic converter, an external start-up clutch, or any othersuitable external start-up element. It is also conceivable to perform astart-up using a start-up element integrated in the transmission.Preferably, a shift element that is actuated in the first forward gearand in the reverse gear is suitable.

Moreover, the multi-step transmission, according to the invention,results in good efficiency in the main drive gears with respect to draglosses and gearing losses.

Furthermore, low moments are present in the shift elements and in theplanetary gear sets of the multi-step transmission, therebyadvantageously reducing wear in the multi-step transmission. Inaddition, the low moments make it possible to utilize correspondinglylow dimensions, thereby reducing the necessary installation space andrelated costs. Furthermore, the rotational speeds of the shafts, shiftelements, and planetary gear sets are low.

In addition, the transmission, according to the invention, is designedto allow adaptability to different drive train embodiments in terms ofpower flow direction and spatial aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail in the following, as anexample, with reference to the attached figures. They show:

FIG. 1: a schematic view of a first preferred embodiment of a multi-steptransmission according to the invention;

FIG. 2: a schematic view of a second preferred embodiment of amulti-step transmission according to the invention; and

FIG. 3: an example of a shift pattern for a multi-step transmissionaccording to FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a multi-step transmission, according to the invention,which has a drive shaft 1, an output shaft 2, and four planetary gearsets P1, P2, P3 and P4 which are disposed in a housing G. Planetary gearsets P1, P2, P3 and P4, in the example shown in FIG. 1, are designed asminus planetary gear sets. According to the invention, at least oneplanetary gear set can be implemented as a plus planetary gear set ifthe carrier and ring gear connection are exchanged and, simultaneously,the value of the stationary transmission ratio is increased by 1 incomparison to the embodiment as a minus planetary gear set.

In the embodiment shown, the planetary gear sets, viewed axially, aredisposed in the sequence P1, P2, P3 and P4.

As shown in FIG. 1, six shift elements are provided, namely, two brakes,03, 04 and four clutches 13, 27, 28 and 35. The spatial disposition ofthe shift elements can be arbitrary, and is limited only by thedimensions of the outer design. The clutches and the brakes of thetransmission are preferably implemented as friction shift elements orlamellar shift elements.

Selective shifting of nine forward gears and one reverse gear can berealized using these shift elements. The multi-step transmission,according to the invention, has a total of eight rotatable shafts,namely, the shafts 1, 2, 3, 4, 5, 6, 7 and 8, wherein the drive shaft isthe first shaft, and the output shaft is the second shaft of thetransmission.

According to the invention, the sun gear of the first planetary gear setP1 is connected to the drive shaft 1 of the multi-step transmission, asshown in FIG. 1, wherein the carrier of the first planetary gear set P1is connected to the third shaft 3 which can be coupled, via a firstbrake 03, to a housing G of the transmission, and is detachablyconnectable, via a first clutch 13, to the drive shaft 1, and, via asecond clutch 35, to the fifth shaft 5. By engaging the first clutch 13,the first planetary gear set P1 can be blocked by coupling the sun gearto the carrier.

As shown in FIG. 1, the fifth shaft 5 is connected to the ring gear ofthe second planetary gear set P2, to the sun gear of the third planetarygear set P3, and to the sun gear of the fourth planetary gear set P4,wherein the drive shaft 1 is connected to the carrier of the fourthplanetary gear set P4.

According to the invention, as shown in FIG. 1 the ring gear of thefirst planetary gear set P1 is connected to the sixth shaft 6 which isconnected to the carrier of the second planetary gear set P2, the ringgear of the third planetary gear set P3 is coupled to a housing G of thetransmission (shaft 0), and the sun gear of the second planetary gearset P2 is connected to the fourth shaft 4, which can be coupled to ahousing of the transmission G via a second brake 04. In the embodimentshown, the output shaft 2 is detachably connectable, via a fourth clutch28, to the eighth shaft 8 which is connected to the carrier of the thirdplanetary gear set P3, and, via a third clutch 27, to the seventh shaft7 which is connected to the ring gear of the fourth planetary gear setP4.

The first clutch 13 and second clutch 35, viewed axially, can bearranged between the first and second planetary gear sets P1, P2. Thethird clutch 27 and fourth clutch 28, viewed axially, can be preferablyarranged between the third and fourth planetary gear sets P3, P4.

The embodiment shown in FIG. 2 differs from the embodiment in FIG. 1 inthat the first clutch is designed as a clutch 36 via which the thirdshaft 3 is detachably connectable to the sixth shaft 6 thereby enablingthe first planetary gear set P1 to be blocked by coupling the carrier ofthe first planetary gear set P1 to the ring gear of the first planetarygear set P1.

FIG. 3 shows an example of a shift pattern of a multi-step transmissionaccording to FIG. 1. Three shift elements are engaged for every gear.The shift pattern shows, as examples, the particular transmission ratiosi of the individual gear steps, and, to be determined therefrom, thegear increments or step changes phi to the next higher gear, wherein thevalue 8.999 is the transmission ratio spread.

Typical values for the stationary transmission ratios of the planetarygear sets P1, P2, P3 and P4 implemented as minus planetary gear sets are−1.953, —2.191, −2.235 and −2.404, respectively. FIG. 3 shows thatdouble shifting or group shifting is avoided when shifting sequentiallysince two adjacent gear steps share two shift elements. It is also shownthat a large transmission ratio spread is attained with small gearincrements.

The first forward gear is attained by engaging the second brake 04 andthe second and fourth clutches 35, 28; the second forward gear isattained by engaging the first, second and fourth clutches 13, 35, 28;the third forward gear is attained by engaging the second brake 04 andthe first and fourth clutches 13, 28; the fourth forward gear isattained by engaging the second brake 04 and the third and fourthclutches 27, 28; the fifth forward gear is attained by engaging thesecond brake 04 and the first and third clutches 13, 27; the sixthforward gear, which is preferably implemented as direct drive, isattained by engaging the first, second and third clutch 13, 35, 27; theseventh forward gear is attained by engaging the second brake 04 and thesecond and third clutches 35, 27; the eighth forward gear is attained byengaging the first brake 03 and the second and third clutches 35, 27;and the ninth forward gear is attained by engaging the first and secondbrakes 03, 04 and the third clutch 27, wherein the reverse gear isattained by engaging the first and second brakes 03, 04 and the fourthclutch 28.

Since the second brake 04 and the fourth clutch 28 are engaged in thefirst forward gear and in the reverse gear, these shift elements can beused as start-up elements.

For the case in which, according to the embodiment depicted in FIG. 2,the first clutch is designed as a clutch 36 via which the third shaft 3can be detachably connected to the sixth shaft 6, the speeds indicatedin the shift pattern shown in FIG. 3 are attained with the differencethat reference character 13 is replaced by reference character 36.

According to the invention, different gear increments can also resultfrom the same gear pattern depending on the shift logic, thereby makingit possible to realize an application-specific or vehicle-specificvariation.

According to the invention, it is possible to provide additionalfreewheels at each suitable location of the multi-step transmission, forexample, between a shaft and the housing, or possibly to connect twoshafts.

According to the invention, an axle differential and/or a distributordifferential can be disposed on the drive side or on the output side.

Within the scope of an advantageous development, the drive shaft 1 canbe separated from a drive motor, as needed, by a clutch element, whereina hydrodynamic converter, a hydraulic clutch, a dry start-up clutch, awet start-up clutch, a magnetic powder clutch, or a centrifugal clutchcan be used as the clutch element. It is also possible to dispose such astart-up element in the power flow direction after the transmissionwherein, in this case, the drive shaft 1 is continuously connected tothe crankshaft of the engine.

The multi-step transmission, according to the invention, also makes itpossible to situate a torsional-vibration damper between the engine andthe transmission.

Within the scope of a further, embodiment of the invention (not shown) awear-free brake, for instance, a hydraulic or electric retarder or thelike, can be disposed on each shaft, preferably on the drive shaft 1 orthe output shaft 2, which is of special significance for use incommercial vehicles in particular. Furthermore, a power take-off drivecan be provided on each shaft, preferably on the drive shaft 1 or theoutput shaft 2, for driving additional assemblies.

The friction shift elements that are used can be designed as powershiftable clutches or brakes. In particular, force locking clutches orbrakes can be used, for instance, lamellar clutches, band brakes, and/orcone clutches.

A further advantage of the multi-step transmission presented here isthat an electric machine can be attached to each shaft as a generatorand/or as an additional drive machine.

Obviously, any structural embodiment, in particular any spatialdisposition of the planetary gear sets and the shift elementsindividually and relative to each other, and insofar as it istechnically expedient, falls under the scope of protection of thepresent claims, without influencing the function of the transmission asspecified in the claims, even if these embodiments are not explicitlyrepresented in the figures or in the description.

REFERENCE CHARACTERS

-   1 First shaft, drive shaft-   2 Second shaft, output shaft-   3 Third shaft-   4 Fourth shaft-   5 Fifth shaft-   6 Sixth shaft-   7 Seven shaft-   8 Eighth shaft-   03 First brake-   04 Second brake-   13 First clutch-   27 Third clutch-   28 Fourth clutch-   35 Second clutch-   36 First clutch-   P1 First planetary gear set-   P2 Second planetary gear set-   P3 Third planetary gear set-   P4 Fourth planetary gear set-   i Transmission ratio-   phi Gear step change-   G Housing

1-4. (canceled)
 5. A multi-step transmission of a planetary design foran automatic transmission for a motor vehicle, the multi-steptransmission comprising: a drive shaft (1); an output shaft (2); first,second, third and fourth planetary gear sets (P1, P2, P3, P4) which aredisposed within a housing (G); and a rotatable third shaft (3), arotatable fourth shaft (4), a rotatable fifth shaft (5), a rotatablesixth shaft (6), a rotatable seventh shaft (7) and a rotatable eighthshaft (8) and at least six shift elements (03, 04, 13, 27, 28, 35, 36)comprising first and second brakes (03, 04) and first, second, third andfourth clutches (13, 27, 28, 35, 36) whose selected engagement producesdifferent transmission ratios between the drive shaft (1) and the outputshaft (2) so that nine forward gears and a reverse gear can be achieved;wherein a sun gear of the first planetary gear set (P1) is connected tothe drive shaft (1), a carrier of the first planetary gear set (P1) isconnected to the third shaft (3) which is connectable to the housing (G)of the transmission via the first brake (03) and is detachablyconnectable to the fifth shaft (5) via the second clutch (35); the fifthshaft (5) is connected to a ring gear of the second planetary gear set(P2), to a sun gear of the third planetary gear set (P3) and to a sungear of the fourth planetary gear set (P4), and the drive shaft (1) isconnected to a carrier of the fourth planetary gear set (P4); the sixthshaft (6) is connected to a ring gear of the first planetary gear set(P1) and to a carrier of the second planetary gear set (P2); a sun gearof the second planetary gear set (P4) is connected to the fourth shaft(4) which is connectable, via the second brake (04), to the housing (G)of the transmission; a ring gear of the third planetary gear set (P3) iscoupled to the housing (G) of the transmission; the output shaft (2) isdetachably connectable, via the fourth clutch (28), to the eighth shaft(8) which is connected to a carrier of the third planetary gear set (P3)and, via the third clutch (27), to the seventh shaft (7) which isconnected to a ring gear of the fourth planetary gear set (P4); and thefirst planetary gear set (P1) can be blocked by engagement of the firstclutch (13 or 36).
 6. The multi-step transmission according to claim 5,wherein the first clutch (13 or 36) one of detachably connects the thirdshaft (3) to the drive shaft (1), and detachably connects the thirdshaft (3) to the sixth shaft (6).
 7. The multi-step transmissionaccording to claim 5, wherein the first, the second, the third and thefourth planetary gear sets (P1, P2, P3, P4) are each minus planetarygear sets.
 8. The multi-stage transmission according to claim 5, whereina first forward gear is attained by engagement of the second brake (04)and the second and the fourth clutches (35, 28); a second forward gearis attained by engagement of the first, the second and the fourthclutches (13 and 36, 35, 28); a third forward gear is attained byengagement of the second brake (04) and the first and the fourthclutches (13 and 36, 28); a fourth forward gear is attained byengagement of the second brake (04) and the third and the fourthclutches (27, 28); a fifth forward gear is attained by engagement of thesecond brake (04) and the first and the third clutches (13 and 36, 27);a sixth forward gear is attained by engagement of the first, the secondand the third clutched (13 and 36, 35, 27); a seventh forward gear isattained by engagement of the second brake (04) and the second and thethird clutches (35, 27); an eighth forward gear is attained byengagement of the first brake (03) and the second and the third clutches(35, 27); a ninth forward gear is attained by engagement of the firstand the second brakes (03, 04) and the third clutch (27); and thereverse gear is attained by engagement of the first and the secondbrakes (03, 04) and the fourth clutch (28).